Biosensing Intestinal Alkaline Phosphatase by Pregnancy Test Strips Based on Target-Triggered CRISPR-Cas12a Activity to Monitor Intestinal Inflammation

With an increasing incidence worldwide, inflammatory bowel disease (IBD) is a chronic inflammatory disease affecting the gastrointestinal tract, which impairs the life quality of patients. Therefore, it is of great significance to construct a sensitive, simple, and convenient biosensor to analyze IBD-associated biomarkers for an auxiliary diagnosis of IBD. Intestinal alkaline phosphatase (IAP), expressed by the intestinal epithelium, is an endogenous protein that is thought to play a vital role in maintaining intestinal homeostasis and is considered a potential biomarker for IBD. Here, an IAP detection method was developed using pregnancy test strips by dephosphorylation. Initially, a double-stranded DNA (dsDNA) was designed to respond to IAP and acted as an activator of Cas12a. In the presence of IAP, the designed dsDNA was not digested by lambda exonuclease (λ exo), which hybridized to the Cas12a-crRNA duplex and resulted in the activation of the trans-cleavage of Cas12a. Further, the activated Cas12a cleaved the single-strand DNA (ssDNA) linker in the MBs-ssDNA-hCG probe, triggering the release of hCG. With magnetic separation, the released hCG could be quantitatively detected by pregnancy test strips. IAP levels were analyzed in feces from colitis and healthy mice by pregnancy test strips. The results showed that the IAP level of colitis mice (3.89 ± 1.92 U/L) was much lower than that of healthy mice (39.64 ± 24.93 U/L), indicating the correlation between IAP and intestinal inflammation. Taken together, a sensitive, user-friendly detection assay based on pregnancy test strips was constructed to monitor IAP and used as an auxiliary diagnostic approach for IBD in a clinical scene.